In many types of electronic apparatus a momentary interruption in the power supplied by a power supply, whether battery or other supply, can cause deleterious effects when the power is restored. For example, some electronic apparatus fails to restart properly, or fails to return to the pre-interruption state after the power supply is restored. This is especially true, for example, in an electronic apparatus that includes and requires precise reference supplies, such as reference voltages and reference currents. As a specific example, battery operated portable cellular telephones can experience an interruption in service if the battery power supply is momentarily disconnected from the telephone. A momentary interruption in the power supply can occur, for example, if a cellular phone that is turned on and is in the standby mode is accidentally dropped causing a momentary disconnection of the battery from the telephone. Similarly, a momentary battery disconnect can occur if the cellular telephone is thrust into a pocket, purse, briefcase, belt holder, or the like.
Again, considering a battery powered portable cellular telephone as a specific example, upon disconnection of the battery from the telephone, the voltage level within the cellular telephone drops, with the rate of drop largely dependent upon the capacitive loading and hence the time constant of the internal circuitry. If the power is restored before the internal voltage falls to a value below which the internal references fail to operate, the cellular telephone will return to its operating state without further interruption of service. Similarly, if the battery interruption is terminated after the internal voltages have dropped to a level below the power on reset (POR) level, the internal circuitry will properly reset and the phone operation will restart. If, however, the battery power is restored after the internal voltage falls to a level below the minimum at which functionality of the references is maintained but above the POR level, one of several undesired results may occur. One result may be that the references will turn off causing the telephone to turn off and stay off. Alternatively, the references may become ineffective, causing analog circuitry within the phone to fail to function properly. If that happens, upon power restoration the telephone may be reset in an unknown and nonfunctional state.
Although a number of solutions have been proposed for the problem of temporary interruption of power supply, these solutions have not been deemed acceptable. Some solutions, for example, require additional expensive circuitry or additional components. Further, some solutions cause a noticeable "OFF" state for the apparatus that is unacceptable for customer use.
In view of the foregoing problem, a need exists for a system and a method for handling a momentary interruption in the power supplied to an electronic apparatus such that upon restoration of the power, operation of the apparatus would be restored without noticeable impact upon the user of the apparatus. The system and method should not require additional external components and should not result in a greatly increased current drain.